<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title>getElementsByTagName获取checkbox进行全选</title>
		<style type="text/css">
			#myTable{ width: 900px; margin: 0px auto; background-color: #008000;}
			#myTable td,#myTable th{ background-color: white;}
			#myDiv{width: 900px; margin: 0px auto; height: 30px; line-height: 30px; 
			text-align: center;}
		</style>
		<!-- <script>======代码======</script> -->
	</head>
	<body>
		<table cellspacing="1" id="myTable">
			<tr>
				<th width="200">
                  <input type="checkbox" id="selAll" onchange="allclick()" />全选
				<input type="checkbox" id="selAll" onchange="changeclick()" />反选
                        </th>
				<th width="200">姓名</th>
				<th width="200">性别</th>
				<th width="200">专业</th>
				<th width="200">爱好</th>
			</tr>
			<tr>
				<td><input type="checkbox"/></td>
				<td>刘备</td>
				<td>男</td>
				<td>软件开发</td>
				<td>抽烟</td>
			</tr>
			<tr>
				<td><input type="checkbox"/></td>
				<td>关羽</td>
				<td>男</td>
				<td>国际贸易</td>
				<td>喝酒</td>
			</tr>
			<tr>
				<td><input type="checkbox"/></td>
				<td>张飞</td>
				<td>男</td>
				<td>园林设计</td>
				<td>烫头发</td>
			</tr>
			<tr>
				<td><input type="checkbox"/></td>
				<td>赵云</td>
				<td>男</td>
				<td>平面设计</td>
				<td>抽烟</td>
			</tr>
			<tr>
				<td><input type="checkbox"/></td>
				<td>黄忠</td>
				<td>男</td>
				<td>影视制作</td>
				<td>玩游戏</td>
			</tr>
			<tr>
				<td><input type="checkbox"/></td>
				<td>小乔</td>
				<td>女</td>
				<td>高级护理</td>
				<td>唱歌</td>
			</tr>
		</table>
		<script>
			

			function changeclick() {
				var input = document.querySelectorAll('input')
				console.log(input);
				var num=0
				for (let i = 2; i < input.length; i++) {
					if (input[i].checked) {
                		input[i].checked = false;
						num++
            		} else {
                		input[i].checked = true;
            		}				
				}
				if (num==input.length-2) {
					input[0].checked=false
				}else if(num==0){
					input[0].checked=true
				}
			}

			function allclick(){
				var input = document.querySelectorAll('input');
				var num=0;
				for (let i = 2; i < input.length; i++) {
					input[i].checked?num++:input[i].checked = true
				}
				if(num==input.length-2){
					changeclick()
				}
			}
		</script>
	</body>
</html>